nonlinear diffusion. porous medium and fast diffusion. …nonlinear diffusion. porous medium and...

Nonlinear Diffusion.Porous Medium and Fast Diffusion.

From Analysis to Physics andGeometry

Juan Luis V azquez

Departamento de Matematicas

Universidad Autonoma de Madrid

♠ LMS-EPSRC Summer Course Swansea, July 2008 ♠

Juan L. Vazquez - Nonlinear Diffusion. Porous Medium and Fast Diffusion Equations – p. 1/??

IntroductionMain topic after 1981: Nonlinear Diffusion



Particular topics: Porous Medium and Fast Diffusion flows




Aim: to develop a complete mathematical theory with sound

physical basis

The resulting theory involves PDEs, Functional Analysis, Inf. Dim. Dyn.

Systems; Diff. Geometry and Probability





physical basis



H. Brezis, Ph. Bénilan

D. G. Aronson, L. A. Caffarelli

L. A. Peletier, S. Kamin, G. Barenblatt, V. A. Galaktionov





physical basis



H. Brezis, Ph. Bénilan

D. G. Aronson, L. A. Caffarelli

L. A. Peletier, S. Kamin, G. Barenblatt, V. A. Galaktionov

+ M. Crandall, L. Evans, A. Friedman, C. Kenig,...


I. DiffusionPopulations diffuse, substances (like particles in a solvent)diffuse, heat propagates, electrons and ions diffuse, themomentum of a viscous (Newtonian) fluid diffuses (linearly),there is diffusion in the markets, ...• what is diffusion anyway?• how to explain it with mathematics?• A main question is: how much of it can be explained with linearmodels, how much is essentially nonlinear?• The stationary states of diffusion belong to an important world, ellipticequations. Elliptic equations, linear and nonlinear, have many relatives:diffusion, fluid mechanics, waves of all types, quantum mechanics, ...


The heat equation originsWe begin our presentation with the Heat Equationut = ∆u and the analysis proposed by Fourier, 1807, 1822

(Fourier decomposition, spectrum). The mathematical modelsof heat propagation and diffusion have made great progressboth in theory and application. They have had a stronginfluence on the 5 areas of Mathematics already mentioned.


The heat equation originsWe begin our presentation with the Heat Equationut = ∆u and the analysis proposed by Fourier, 1807, 1822

(Fourier decomposition, spectrum). The mathematical modelsof heat propagation and diffusion have made great progressboth in theory and application. They have had a stronginfluence on the 5 areas of Mathematics already mentioned.

The heat flow analysis is based on two main techniques:

integral representation (convolution with a Gaussian kernel)

and mode separation:

u(x, t) =∑

Ti(t)Xi(x)

where the Xi(x) form the spectral sequence

−∆Xi = λi Xi.This is the famous linear eigenvalue problem


Linear heat flowsFrom 1822 until 1950 the heat equation has motivated

(i) Fourier analysis decomposition of functions (and set theory),

(ii) development of other linear equations

=⇒ Theory of Parabolic Equations

ut =∑

aij∂i∂ju +∑

bi∂iu + cu + f






ut =∑

aij∂i∂ju +∑

bi∂iu + cu + f

Main inventions in Parabolic Theory:

(1) aij , bi, c, f regular ⇒ Maximum Principles, Schauder

estimates, Harnack inequalities; Cα spaces (Hölder); potential

theory; generation of semigroups.(2) coefficients only continuous or bounded ⇒ W 2,p estimates,Calderón-Zygmund theory, weak solutions; Sobolev spaces.






ut =∑

aij∂i∂ju +∑

bi∂iu + cu + f

Main inventions in Parabolic Theory:

(1) aij , bi, c, f regular ⇒ Maximum Principles, Schauder

estimates, Harnack inequalities; Cα spaces (Hölder); potential

theory; generation of semigroups.(2) coefficients only continuous or bounded ⇒ W 2,p estimates,Calderón-Zygmund theory, weak solutions; Sobolev spaces.

The probabilistic approach: Diffusion as an stochasticprocess: Bachelier, Einstein, Smoluchowski, Wiener, Levy, Ito,...

dX = bdt + σdW


Nonlinear heat flows

In the last 50 years emphasis has shifted towards the Nonlinear

World. Maths more difficult, more complex and more realistic.

My group works in the areas of Nonlinear Diffusion and

Reaction Diffusion.

I will present an overview and recent results in the theory

mathematically called Nonlinear Parabolic PDEs. General

formula

ut =∑

∂iAi(u,∇u) +∑

B(x, u,∇u)


Nonlinear heat flows

In the last 50 years emphasis has shifted towards the Nonlinear

World. Maths more difficult, more complex and more realistic.

My group works in the areas of Nonlinear Diffusion and

Reaction Diffusion.

I will present an overview and recent results in the theory

mathematically called Nonlinear Parabolic PDEs. General

formula

ut =∑

∂iAi(u,∇u) +∑

B(x, u,∇u)

Typical nonlinear diffusion: ut = ∆um

Typical reaction diffusion: ut = ∆u + up


The Nonlinear Diffusion ModelsThe Stefan Problem (Lamé and Clapeyron, 1833; Stefan 1880)

SE :

ut = k1∆u for u > 0,

ut = k2∆u for u < 0.TC :

u = 0,

v = L(k1∇u1 − k2∇u2).

Main feature: the free boundary or moving boundary where

u = 0. TC= Transmission conditions at u = 0.



SE :



u = 0,

v = L(k1∇u1 − k2∇u2).



The Hele-Shaw cell (Hele-Shaw, 1898; Saffman-Taylor, 1958)

u > 0, ∆u = 0 in Ω(t); u = 0, v = L∂nu on ∂Ω(t).



SE :



u = 0,

v = L(k1∇u1 − k2∇u2).





The Porous Medium Equation →(hidden free boundary)

ut = ∆um, m > 1.



SE :



u = 0,

v = L(k1∇u1 − k2∇u2).





The Porous Medium Equation →(hidden free boundary)

ut = ∆um, m > 1.

The p-Laplacian Equation, ut = div (|∇u|p−2∇u).


The Reaction Diffusion ModelsThe Standard Blow-Up model (Kaplan, 1963; Fujita, 1966)

ut = ∆u + up

Main feature: If p > 1 the norm ‖u(·, t)‖∞ of the solutions goes

to infinity in finite time. Hint: Integrate ut = up.

Problem: what is the influence of diffusion / migration?



ut = ∆u + up




General scalar model

ut = A(u) + f(u)



ut = ∆u + up





ut = A(u) + f(u)

The system model: −→u = (u1, · · · , um) → chemotaxis.



ut = ∆u + up





ut = A(u) + f(u)


The fluid flow models: Navier-Stokes or Euler equation

systems for incompressible flow. Any singularities?



ut = ∆u + up





ut = A(u) + f(u)


The fluid flow models: Navier-Stokes or Euler equation

systems for incompressible flow. Any singularities?

The geometrical models: the Ricci flow: ∂tgij = −Rij .


An opinion of John Nash, 1958:

The open problems in the area of nonlinear p.d.e. arevery relevant to applied mathematics and science as awhole, perhaps more so that the open problems in anyother area of mathematics, and the field seems poised forrapid development. It seems clear, however, that freshmethods must be employed...

Little is known about the existence, uniqueness andsmoothness of solutions of the general equations of flow fora viscous, compressible, and heat conducting fluid...

“Continuity of solutions of elliptic and parabolic equations”,paper published in Amer. J. Math, 80, no 4 (1958), 931-954


II. Porous Medium Diffusion

ut = ∆um = ∇ · (c(u)∇u)

density-dependent diffusivity

c(u) = mum−1[= m|u|m−1]

degenerates at u = 0 if m > 1


Applied motivation for the PMEFlow of gas in a porous medium (Leibenzon, 1930; Muskat

1933) m = 1 + γ ≥ 2

ρt + div (ρv) = 0,

v = − kµ∇p, p = p(ρ).

Second line left is the Darcy law for flows in porous media (Darcy,

1856). Porous media flows are potential flows due to averaging of Navier-Stokes

on the pore scales.

To the right, put p = po ργ , with γ = 1 (isothermal), γ > 1 (adiabatic

flow).

ρt = div (k

µρ∇p) = div (

k

µρ∇(poρ

γ)) = c∆ργ+1.


Applied motivation for the PMEFlow of gas in a porous medium (Leibenzon, 1930; Muskat

1933) m = 1 + γ ≥ 2

ρt + div (ρv) = 0,

v = − kµ∇p, p = p(ρ).

Second line left is the Darcy law for flows in porous media (Darcy,

1856). Porous media flows are potential flows due to averaging of Navier-Stokes

on the pore scales.

To the right, put p = po ργ , with γ = 1 (isothermal), γ > 1 (adiabatic

flow).

ρt = div (k

µρ∇p) = div (

k

µρ∇(poρ

γ)) = c∆ργ+1.

Underground water infiltration (Boussinesq, 1903) m = 2


Applied motivation IIPlasma radiation m ≥ 4 (Zeldovich-Raizer, < 1950)

Experimental fact: diffusivity at high temperatures is not constant as

in Fourier’s law, due to radiation.

d

dt

∫

ΩcρT dx =

∫

∂Ωk(T )∇T · ndS.

Put k(T ) = koTn, apply Gauss law and you get

cρ∂T

∂t= div(k(T )∇T ) = c1∆Tn+1.

→ When k is not a power we get Tt = ∆Φ(T ) with Φ′(T ) = k(T ).





d

dt

∫

ΩcρT dx =

∫



cρ∂T

∂t= div(k(T )∇T ) = c1∆Tn+1.


Spreading of populations (self-avoiding diffusion) m ∼ 2.





d

dt

∫

ΩcρT dx =

∫



cρ∂T

∂t= div(k(T )∇T ) = c1∆Tn+1.



Thin films under gravity (no surface tension) m = 4.





d

dt

∫

ΩcρT dx =

∫



cρ∂T

∂t= div(k(T )∇T ) = c1∆Tn+1.




Kinetic limits (Carleman models, McKean, PL Lions and Toscani et al.)





d

dt

∫

ΩcρT dx =

∫



cρ∂T

∂t= div(k(T )∇T ) = c1∆Tn+1.




Kinetic limits (Carleman models, McKean, PL Lions and Toscani et al.)

Many more (boundary layers, geometry).Juan L. Vazquez - Nonlinear Diffusion. Porous Medium and Fast Diffusion Equations – p. 19/??

The basicsThe equation is re-written for m = 2 as

12ut = u∆u + |∇u|2



12ut = u∆u + |∇u|2

and you can see that for u ∼ 0 it looks like the eikonal equation

ut = |∇u|2

This is not parabolic, but hyperbolic (propagation along characteristics).

Mixed type, mixed properties.



12ut = u∆u + |∇u|2

and you can see that for u ∼ 0 it looks like the eikonal equation

ut = |∇u|2

This is not parabolic, but hyperbolic (propagation along characteristics).

Mixed type, mixed properties.

No big problem when m > 1, m 6= 2. The pressure

transformation gives:

vt = (m − 1)v∆v + |∇v|2

where v = cum−1 is the pressure; normalization c = m/(m − 1).

This separates m > 1 PME - from - m < 1 FDE


Planning of the Theory

These are the main topics of mathematical analysis (1958-2006):

The precise meaning of solution.





The nonlinear approach: estimates; functional spaces.






Existence, non-existence. Uniqueness, non-uniqueness.







Regularity of solutions: is there a limit? Ck for some k?








Regularity and movement of interfaces: Ck for some k?.









Asymptotic behaviour: patterns and rates? universal?










The probabilistic approach. Nonlinear process. Wasserstein estimates










The probabilistic approach. Nonlinear process. Wasserstein estimates

Generalization: fast models, inhomogeneous media,

anisotropic media, applications to geometry or image

processing; other effects.


Barenblatt profiles (ZKB)These profiles are the alternative to the Gaussian profiles.



They are source solutions. Source means that u(x, t) → M δ(x) as

t → 0.




t → 0.

Explicit formulas (1950):(

α = n2+n(m−1)

, β = 12+n(m−1)

< 1/2)

B(x, t;M) = t−αF(x/tβ), F(ξ) =

(

C − kξ2)1/(m−1)

+




t → 0.


α = n2+n(m−1)

, β = 12+n(m−1)

< 1/2)


(

C − kξ2)1/(m−1)

+

x

u

BS




t → 0.


α = n2+n(m−1)

, β = 12+n(m−1)

< 1/2)


(

C − kξ2)1/(m−1)

+

x

u

BS

Height u = Ct−α Free boundary at distance |x| = ctβ

Scaling law; anomalous diffusion versus Brownian motion


FDE profilesWe again have explicit formulas for 1 > m > (n − 2)/n:


1

(C + kξ2)1/(1−m)

x

u(⋅,t) t=1.15t=1.25t=1.4t=1.6

α = n2−n(1−m)

β = 12−n(1−m)

> 1/2

Solutions for m > 1 with fat tails (polynomial decay; anomalous distributions)


FDE profilesWe again have explicit formulas for 1 > m > (n − 2)/n:


1

(C + kξ2)1/(1−m)

x

u(⋅,t) t=1.15t=1.25t=1.4t=1.6

α = n2−n(1−m)

β = 12−n(1−m)

> 1/2

Solutions for m > 1 with fat tails (polynomial decay; anomalous distributions)

Big problem: What happens for m < (n − 2)/n? Most active branchof PME/FDE. New asymptotics, extinction, new functional properties, new geometryand physics.Many authors: J. King, geometers, ... → my book “Smoothing”.


Concept of solution

There are many concepts of generalized solution of the PME:

Classical solution: only in nondegenerate situations, u > 0.


Concept of solution



Limit solution: physical, but depends on the approximation (?).


Concept of solution



Limit solution: physical, but depends on the approximation (?).

Weak solution Test against smooth functions and eliminate

derivatives on the unknown function; it is the mainstream; (Oleinik,

1958)∫ ∫

(u ηt −∇um · ∇η) dxdt +

∫

u0(x) η(x, 0) dx = 0.

Very weak∫ ∫

(u ηt + um ∆η) dxdt +

∫

u0(x) η(x, 0) dx = 0.


More on concepts of solutionSolutions are not always weak:

Strong solution. More regular than weak but not classical: weakderivatives are Lp functions. Big benefit: usual calculus is possible.




Semigroup solution / mild solution. The typical product of functionaldiscretization schemes: u = unn, un = u(·, tn),

ut = ∆Φ(u),un − un−1

h− ∆Φ(un) = 0




Semigroup solution / mild solution. The typical product of functionaldiscretization schemes: u = unn, un = u(·, tn),

ut = ∆Φ(u),un − un−1

h− ∆Φ(un) = 0

Now put f := un−1, u := un, and v = Φ(u), u = β(v):

−h∆Φ(u) + u = f, −h∆v + β(v) = f.

"Nonlinear elliptic equations"; Crandall-LiggettTheorems Ambrosio, Savarè, Nochetto


More on concepts of solution II

Solutions of more complicated equations need new concepts:

Viscosity solution Two ideas: (1) add artificial viscosity and pass to

the limit; (2) viscosity concept of Crandall-Evans-Lions (1984);

adapted to PME by Caffarelli-Vazquez (1999).







Entropy solution (Kruzhkov, 1968). Invented for conservation laws;

it identifies unique physical solution from spurious weak solutions. It

is useful for general models degenerate diffusion-convection models;










Renormalized solution (Di Perna - Lions).











BV solution (Volpert-Hudjaev).











BV solution (Volpert-Hudjaev).

Kinetic solutions (Perthame,...).


The main estimatesBoundedness estimates: for every p ≥ 1

Ip(t) =

∫

Rn

up(x, t) dx ≤ Ip(0)

and goes down with time



Ip(t) =

∫

Rn



Derivative estimates for compactness: The basic L2 space

estimate

1

m + 1

∫∫

QT

|∇um|2 dxdt +

∫

Ω

|u(x, t)|m+1dx =

∫

Ω

|u0|m+1dx

Idea: multiplier is um



Ip(t) =

∫

Rn



Derivative estimates for compactness: The basic L2 space

estimate

1

m + 1

∫∫

QT

|∇um|2 dxdt +

∫

Ω

|u(x, t)|m+1dx =

∫

Ω

|u0|m+1dx

Idea: multiplier is um

The time derivative estimate.

c

∫∫

QT

|(u(m+1)/2)t |2 dxdt +

∫

Ω

|∇u(x, t)m|2dx =

∫

Ω

|∇u0(x)m|2dx

Idea: multiplier is (um)t


The L1 estimate. Contraction. Existence

Problem: They are not stability estimates for differences.




The main stability estimate (L1 contraction):

d

dt

∫

Ω|u1(x, t) − u2(x, t)| dx ≤ 0





d

dt

∫

Ω|u1(x, t) − u2(x, t)| dx ≤ 0

Proof. Multiply the difference of the equations for u1 and u2 by ζ = hǫ(w), where hǫ is

a smooth version of Heaviside’s step function, and w = um1 − um

2 , u = u1 − u2. Then,

∫

ut h(w) dx =

∫

∆w h(w) dx = −

∫

h′(w)|∇w|2 dx ≤ 0.

Now let hǫ → h = sign +. Observe that sign (u1 − u2) = sign (um1 − um

2 ). Then

d

dt

∫

(u1 − u2)+ dx =

∫

ut h(u) dx ≤ 0





d

dt

∫

Ω|u1(x, t) − u2(x, t)| dx ≤ 0

Proof. Multiply the difference of the equations for u1 and u2 by ζ = hǫ(w), where hǫ is

a smooth version of Heaviside’s step function, and w = um1 − um

2 , u = u1 − u2. Then,

∫

ut h(w) dx =

∫

∆w h(w) dx = −

∫

h′(w)|∇w|2 dx ≤ 0.

Now let hǫ → h = sign +. Observe that sign (u1 − u2) = sign (um1 − um

2 ). Then

d

dt

∫

(u1 − u2)+ dx =

∫

ut h(u) dx ≤ 0

Contraction is also true in H−1 and in the Wasserstein W2 space


The standard solutions

Let Ω = Rn or bounded set with zero Dirichlet boundary data,

n ≥ 1, 0 < T ≤ ∞. Let us consider the PME with m > 1.

For every u0 ∈ L1(Ω), u0 ≥ 0, there exists a weak solution such

that u, um ∈ L2x,t and ∇um ∈ L2

x,t.







x,t.

The weak solution is a strong solution in the following sense:

(i) um ∈ L2(τ,∞ : H10 (Ω)) for every τ > 0;

(ii) ut and ∆um ∈ L1loc(0,∞ : L1(Ω)) and ut = ∆um a.e. in Q;

(iii) u ∈ C([0, T ) : L1(Ω)) and u(0) = u0.







x,t.

The weak solution is a strong solution in the following sense:

(i) um ∈ L2(τ,∞ : H10 (Ω)) for every τ > 0;

(ii) ut and ∆um ∈ L1loc(0,∞ : L1(Ω)) and ut = ∆um a.e. in Q;

(iii) u ∈ C([0, T ) : L1(Ω)) and u(0) = u0.

We also have bounded solutions that decay in time

0 ≤ u(x, t) ≤ C‖u0‖2β1 t−α

ultra-contractivity generalized to nonlinear cases


Regularity resultsThe universal estimate holds (Aronson-Bénilan, 79):

∆v ≥ −C/t.

v ∼ um−1 is the pressure.



∆v ≥ −C/t.


(Caffarelli-Friedman, 1982) Cα regularity: there is an α ∈ (0, 1)

such that a bounded solution defined in a cube is Cα

continuous.



∆v ≥ −C/t.




continuous.

If there is an interface Γ, it is also Cα continuous in space time.



∆v ≥ −C/t.




continuous.

If there is an interface Γ, it is also Cα continuous in space time.

How far can you go? Free boundaries are stationary (metastable) ifinitial profile is quadratic near ∂Ω: u0(x) = O(d2). This is calledwaiting time. Characterized by V. in 1983. Visually interesting in thin films

spreading on a table. Existence of corner points possible whenmetastable, → no C1 Aronson-Caffarelli-V. Regularity stops here in n = 1


Free Boundaries in several dimensions

x

t

Region where u(x,t)>0

u=0 u=0 u=0

A complex free boundary in 1-D A regular free boundary in n-D

(Caffarelli-Vazquez-Wolanski, 1987) If u0 has compact support,

then after some time T the interface and the solutions are C1,α.


Free Boundaries in several dimensions

x

t

Region where u(x,t)>0

u=0 u=0 u=0

A complex free boundary in 1-D A regular free boundary in n-D

(Caffarelli-Vazquez-Wolanski, 1987) If u0 has compact support,

then after some time T the interface and the solutions are C1,α.

(Koch, thesis, 1997) If u0 is transversal then FB is C∞ after T .Pressure is “laterally" C∞. it is a broken profile always when it moves.


Free Boundaries II. Holes

A free boundary with a hole in 2D, 3D is the way of showing

that focusing accelerates the viscous fluid so that the speed

becomes infinite. This is blow-up for v ∼ ∇um−1.

The setup is a viscous fluid on a table occupying an annulus of

radii r1 and r2. As time passes r2(t) grows and r1(t) goes to

the origin. As t → T , the time the hole disappears, the speed

r′1(t) → −∞.


Free Boundaries II. Holes

A free boundary with a hole in 2D, 3D is the way of showing

that focusing accelerates the viscous fluid so that the speed

becomes infinite. This is blow-up for v ∼ ∇um−1.

The setup is a viscous fluid on a table occupying an annulus of

radii r1 and r2. As time passes r2(t) grows and r1(t) goes to

the origin. As t → T , the time the hole disappears, the speed

r′1(t) → −∞.

There is a semi-explicit solution displaying that behaviour

u(x, t) = (T − t)αF (x(T − t)−β).

The interface is then r1(t) = a(T − t)β . It is proved that β < 1.Aronson and Graveleau, 1993. Later Angenent, Aronson,...,Vazquez,


III. Asymptotics


Asymptotic behaviourNonlinear Central Limit Theorem

Choice of domain: IRn. Choice of data: u0(x) ∈ L1(IRn). We can write

ut = ∆(|u|m−1u) + f

Let us put f ∈ L1x,t. Let M =

∫

u0(x) dx +∫∫

f dxdt.




ut = ∆(|u|m−1u) + f


∫

u0(x) dx +∫∫

f dxdt.

Asymptotic Theorem [Kamin and Friedman, 1980; V. 2001] LetB(x, t;M) be the Barenblatt with the asymptotic mass M ; uconverges to B after renormalization

tα|u(x, t) − B(x, t)| → 0

For every p ≥ 1 we have

‖u(t) − B(t)‖p = o(t−α/p′

), p′ = p/(p − 1).

Note: α and β = α/n = 1/(2 + n(m − 1)) are the zoomingexponents as in B(x, t).




ut = ∆(|u|m−1u) + f


∫

u0(x) dx +∫∫

f dxdt.

Asymptotic Theorem [Kamin and Friedman, 1980; V. 2001] LetB(x, t;M) be the Barenblatt with the asymptotic mass M ; uconverges to B after renormalization

tα|u(x, t) − B(x, t)| → 0

For every p ≥ 1 we have

‖u(t) − B(t)‖p = o(t−α/p′

), p′ = p/(p − 1).

Note: α and β = α/n = 1/(2 + n(m − 1)) are the zoomingexponents as in B(x, t).

Starting result by FK takes u0 ≥ 0, compact support and f = 0


Asymptotic behaviour. Picture+ The rate cannot be improved without more information on u0

+ m also less than 1 but supercritical (→ with even better convergence called relative errorconvergence)m < (n − 2)/n has big surprises;m = 0 → ut = ∆ log u → Ricci flow with strange properties;

Proof works for p-Laplacian flow


Asymptotic behaviour. IIThe rates. Carrillo-Toscani 2000. Using entropy functionalwith entropy dissipation control you can prove decay rateswhen

∫

u0(x)|x|2 dx < ∞ (finite variance):

‖u(t) − B(t)‖1 = O(t−δ),

We would like to have δ = 1. This problem is still open for m > 2. New results by JA

Carrillo, McCann, Del Pino, Dolbeault, Vazquez et al. include m < 1.


Asymptotic behaviour. IIThe rates. Carrillo-Toscani 2000. Using entropy functionalwith entropy dissipation control you can prove decay rateswhen

∫

u0(x)|x|2 dx < ∞ (finite variance):

‖u(t) − B(t)‖1 = O(t−δ),

We would like to have δ = 1. This problem is still open for m > 2. New results by JA

Carrillo, McCann, Del Pino, Dolbeault, Vazquez et al. include m < 1.

Eventual geometry, concavity and convexity Result byLee and Vazquez (2003): Here we assume compact support.There exists a

time after which the pressure is concave, the domain convex, the level sets convex and

t ‖(D2v(·, t) − kI)‖∞ → 0

uniformly in the support. The solution has only one maximum. Inner Convergence in

C∞.


Calculations of the entropy ratesWe rescale the function as u(x, t) = r(t)n ρ(y r(t), s)

where r(t) is the Barenblatt radius at t + 1, and “new time" iss = log(1 + t). Equation becomes

ρs = div (ρ(∇ρm−1 +c

2∇y2)).





2∇y2)).

Then define the entropy

E(u)(t) =

∫

(1

mρm +

c

2ρy2) dy

The minimum of entropy is identified as the Barenblatt profile.





2∇y2)).

Then define the entropy

E(u)(t) =

∫

(1

mρm +

c

2ρy2) dy

The minimum of entropy is identified as the Barenblatt profile.

Calculate

dE

ds= −

∫

ρ|∇ρm−1 + cy|2 dy = −D

Moreover,dD

ds= −R, R ∼ λD.

We conclude exponential decay of D and E in new time s, which is potential in real

time t.Juan L. Vazquez - Nonlinear Diffusion. Porous Medium and Fast Diffusion Equations – p. 53/??

Asymptotics IV. ConcavityThe eventual concavity results of Lee and Vazquez

010

2030

4050

60

0

10

20

30

40

50

60−0.2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

010

2030

4050

60

0

20

40

60

80

100−0.2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Eventual concavity for PME in 3D and in 1D

010

2030

4050

60

0

10

20

30

400

0.2

0.4

0.6

0.8

1

1.2

1.4

010

2030

4050

60

0

10

20

30

400

0.2

0.4

0.6

0.8

1

1.2

1.4

Eventual concavity for HE Eventual concavity for FDE


ReferencesAbout PME

J. L. Vázquez, "The Porous Medium Equation. MathematicalTheory", Oxford Univ. Press, 2006 in press. approx. 600 pages

About estimates and scaling


ReferencesAbout PME



J. L. Vázquez, “Smoothing and Decay Estimates for NonlinearParabolic Equations of Porous Medium Type”, Oxford Univ. Press,2006, 234 pages.

About asymptotic behaviour. (Following Lyapunov andBoltzmann)


ReferencesAbout PME



J. L. Vázquez, “Smoothing and Decay Estimates for NonlinearParabolic Equations of Porous Medium Type”, Oxford Univ. Press,2006, 234 pages.

About asymptotic behaviour. (Following Lyapunov andBoltzmann)

J. L. Vázquez. Asymptotic behaviour for the Porous MediumEquation posed in the whole space. Journal of Evolution Equations3 (2003), 67–118.


Probabilities. Wasserstein

Definition of Wasserstein distance.

Let P(IRn) be the set of probability measures. Let p > 0. µ1, µ2

probability measures.

(dp(µ1, µ2))p = inf

π∈Π

∫

IRn×IRn

|x − y|p dπ(x, y),

Π = Π(µ1, µ2) is the set of all transport plans that move the

measure µ1 into µ2. This is a distance.

Technically, this means that π is a probability measure on the

product space IRn × IRn that has marginals µ1 and µ2. It can

be proved that we may use transport functions y = T (x)

instead of transport plans (this is Monge’s version of the

transportation problem).


Wasserstein II

In principle, for any two probability measures, the infimum may

be infinite. But when 1 ≤ p < ∞, dp defines a metric on the set

Pp of probability measures with finite p-moments,∫

|x|pdµ < ∞. A convenient reference for this topic is Villani’s

book, “Topics in Optimal Transportation”, 2003.


Wasserstein II

In principle, for any two probability measures, the infimum may

be infinite. But when 1 ≤ p < ∞, dp defines a metric on the set

Pp of probability measures with finite p-moments,∫

|x|pdµ < ∞. A convenient reference for this topic is Villani’s

book, “Topics in Optimal Transportation”, 2003.

The metric d∞ plays an important role in controlling the location

of free boundaries. Definition d∞(µ1, µ2) = infπ∈Π dπ,∞(µ1, µ2),

with

dπ,∞(µ1, µ2) = sup|x − y| : (x, y) ∈ support(π).

In other words, dπ,∞(µ1, µ2) is the maximal distance incurredby the transport plan π, i.e., the supremum of the distances|x − y| such that π(A) > 0 on all small neighbourhoods A of(x, y). We call this metric the maximal transport distance.


Wasserstein IIIThe contraction properties in n = 1

Theorem (Vazquez, 1983, 2004) Let µ1 and µ2 be finite nonnegative

Radon measures on the line and assume that µ1(R) = µ2(R) and

d∞(µ1, µ2) is finite. Let ui(x, t) the continuous weak solution of the PME

with initial data µi. Then, for every t2 > t1 > 0

d∞(u1(·, t2), u2(·, t2)) ≤ d∞(u1(·, t1), u2(·, t1)) ≤ d∞(µ1, µ2).

Theorem (Carrillo, 2004) Contraction holds in dp for all p ∈ [1,∞).







d∞(u1(·, t2), u2(·, t2)) ≤ d∞(u1(·, t1), u2(·, t1)) ≤ d∞(µ1, µ2).


Contraction properties in n > 1

Theorem (McCann, 2003) For the heat equation contraction holds for

all p and n ≥ 1. (Carrillo, McCann, Villani 2004) For the PME

Contraction holds in d2 for all n ≥ 1.







d∞(u1(·, t2), u2(·, t2)) ≤ d∞(u1(·, t1), u2(·, t1)) ≤ d∞(µ1, µ2).


Contraction properties in n > 1

Theorem (McCann, 2003) For the heat equation contraction holds for

all p and n ≥ 1. (Carrillo, McCann, Villani 2004) For the PME

Contraction holds in d2 for all n ≥ 1.

Theorem (Vazquez, 2004) For the PME, contraction does not hold in

d∞ for any n > 1. It does not in dp for p ≥ p(n) > 2.


New fieldsFast diffusion (m < 1)

ut = ∇ · (um−1∇u) = ∇ · (∇u

up)

Geometrical applications: Yamabe flow, m = (n − 2)/n. Extinction.see our book Smoothing



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up)


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